Vehicle drive and steering system

ABSTRACT

979,453. Hydrostatic transmissions. DOWTY HYDRAULIC UNITS Ltd. Aug. 9, 1961 [Aug. 19, 1960]; No. 28812/60. Headings F2C and F2D. [Also in Division G3] Two separate hydrostatic transmissions each comprise a variable displacement pump driving a fixed displacement motor, a common control means being provided for simultaneously varying the displacement of the pumps and means also being provided for selectively varying the displacement of the individual pumps. Tractor engine 1 drives, through gears 2, 3 and 4, two variable displacement hydraulic pumps 5 and 6 which respectively drive hydraulic motors 7 and 12 which drive, through gear trains 8 and 13, sprockets 9 and 14 in driving engagement with endless tracks 11 and 15 respectively. The displacements of pumps 5 and 6 are adjustable by servomotors 16 and 17 (see Division G3), which include projecting control members 18, 19 respectively. A manuallyoperated speed control lever 25 is connected with members 18, 19 through a link 24, yoke 23 and springs 21, 22. Lever 25 also controls a rotary valve 26. Member 28 of the valve has two recesses 29, 31 which co-operate respectively with ports 32, 33, 34 and 36, 37, 38 extending into the bore 35 of the valve. Ports 32, 34, 36, 38 are fed with liquid from an auxiliary pump 42 through restrictors 43 to 46 respectively and are also connected, through pipes 47, 48, 49 and 51, to servomotors 17 and 16 for overriding control thereof. Ports 33, 37 are respectively connected to adjustable leak valves 39, 41. Thus if lever 25 is rotated counterclockwise port 33 is connected to port 34, and port 36 to port 37. Operation of leak valve 39 permits liquid flow from pump 42 through restrictor 44 and reduces pressure in pipe 48 relatively to pipe 47. Thus valve 39 is arranged to apply an overriding control to servo 17 in the direction to reduce the displacement of pump 6. Similarly, operation of valve 41 is arranged to reduce the displacement of pump 5. Thus the tractor speed is adjusted by lever 25 and steering is effected by operation of valves 39, 41. Specification 949,672 is referred to.

Feb. 28, 1967 B. c. KEMPSON 3,306,385

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Feb. 28, 1967 B. c. KEMPSON 3,

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Feb. 28, 1967 c. KEMP N 3,306,385

VEHICLE DRIVE AND STEERING SYSTEM Original Filed Aug. 15, 1961 4Sheets-Sheet 4 FIG. 5.

I71 Vs/v Tm BERTRAM c- KaMP -n United States Patent 3,306,385 VEHICLEDRIVE AND STEERING SYSTEM Bertram Carl Kempson, St. Marks, Cheltenham,England, assignor to Dowty Hydraulic Units Limited, Ashchurch,Tewkesbury, England, a British company Continuation of abandonedapplication Ser. No. 131,522, Aug. 15, 1961. This application Aug. 28,1964, Ser. No. 394,378 Claims priority, application Great Britain, Aug.19, 1960, 28,812/ 60 Claims. (Cl. 180-648) This application is acontinuation of my earlier filed application Serial No. 131,522 of thesame title and filed on August 15, 1961, now abandoned.

This invention relates to control apparatus for dual infinitely variablespeed ratio power transmissions installed in a vehicle to transmit powerfrom a single engine or other power source to ground engaging elementsspaced transversely of the vehicle to obtain vehicle speed control andsteering. The object of the invention is to provide a simplified form ofsuch a control. For the purpose of this specification the term speedratio as applied to a power transmission refers to the ratio of outputspeed to input speed of the transmission. In this invention this willmean for each transmission the ratio between the speed of the groundengaging element driven by the transmission and the power source speed.

In a vehicle having dual infinitely variable power transmissions totransmit power from the vehicle engine or other power source to groundengaging elements spaced transversely of the vehicle the presentinvention comprises a speed control means operable to adjust bothtransmissions similarly so that they have the same speed ratio for thecontrol of vehicle speed, and a pair of steering controls operable oneon each transmission to reduce in an overriding sense the selected speedratio for that transmission without reducing the speed ratio of theother transmission. Thus reduction of the speed ratio of one or othertransmission will determine a curved path of travel for the vehicle. Thesteering controls may be arranged so that speed ratio reduction of atransmission is proportional to movement of the steering control. Asingle manually operable steering member may be mechanically arrangedrelatively to the two steering controls to operate one or the otheralternatively and such a steering member may take the form of theconventional steering wheel. The steering controls may be arranged sothat the reduction in speed ratio of their associated transmissions isproportional to movement over a part only of the steering controlmovement, further movement being arranged to give large reduction inspeed ratio of the associated transmission to enable very acute curvesto be negotiated by the vehicle. The vehicle to which the inventionrelates may be a vehicle having twin endless tracks such for example asa crawler tractor or alternatively it may be a wheeled vehicle intendedfor travelling over rough or yielding ground. The invention is intendedmore particularly to employ hydraulic infinitely variable powertransmissions whose speed ratio is basically determined by a hydraulicservo motor and which may be reduced in an overriding sense for steeringpurposes by a simple variable leak valve.

One example of the invention employing dual hydraulic infinitelyvariable speed ratio transmissions for driving the tracks of a crawlertractor will now be described together with one modification thereofwith reference to the accompanying drawings in which,

FIGURE 1 is a circuit diagram of the control system of the invention,

FIGURES 2 and 3 are cross-section and plan respectively of a steeringcontrol,

FIGURE 4 is a cross-section through a servo motor for adjustment of atransmission speed ratio, and

FIGURE 5 is a modified version showing a simple single control memberfor alternative operation of the two steering controls.

Reference is made initially to FIGURE 1 of the drawings. In thesedrawings the tractor engine 1 is connected to drive a main gear wheel 2with which meshes a pair of gears 3 and 4 individually connected todrive a pair of infinitely variable positive displacement hydraulicpumps 5 and 6. These pumps may have any known constructional form. Thepump 5 is hydraulically connected with a fixed displacement hydraulicmotor 7 which drives through a gear train 8 a sprocket 9 in drivingengagement with one endless track 11 of the tractor. Similarly the pump6 is hydraulically connected to drive a fixed displacement hydraulicmotor 12 which drives through a gear train 13 a sprocket 14 in drivingengagement with the other track 15 of the tractor. Thus pump 5 and motor7 form one transmission whilst pump 6 and motor 12 form the othertransmission. For displacement adjustment each pump 5 and 6 includesrespectively a servo motor 16 or 17 the structure of each of which isshown in detail in FIGURE 4 and will be described later in thisspecification. Each servo motor includes a projecting control memberrespectively 18 and 19, and movement applied to this control member tothe left or to the right from the central position as seen in thedrawings will cause a forward or reverse displacement respectively to beelfected on the associated pump. The controls 18 and 19 are movabletogether by means of a pair of caged spring units 21 and 22 from a yoke23. A link 24 pivotally connected to the yoke 23 extends to a speedcontrol lever 25. For ordinary speed control of the tractor it is merelynecessary to move the lever 25 to the left or to the right as seen inthe drawings to cause corresponding movements of the servo motorcontrols 18 and 19 which will give forward or reverse displacement tothe pumps 5 and 6 and thus driving speeds in the forward or reversesense to the tracks 11 and 15. The displacement of each pump is directlyproportional to the speed ratio of the transmission of which it formspart and that displacement adjustment effects speed ratio adjustment.

Apart from adjusting the pump displacements the lever 25 also rotates acontrol valve 26 which comprises a body 27 having a rotary plug 28therein. The rotary plug includes two opposed recesses 29 and 31. Therecess 29 co-operates with three ports 32, 33 and 34 extending into thebore 35 in which the plug is located. Similarly the recess 31co-operates with three ports 36, 37 and 38 also extending into the bore35. In the zero speed position as indicated in FIGURE 1 recess 29 is incommunication only with port 33 and recess 31 is in communication onlywith port 37. Movement of lever 35 in the forward sense i.e. to the leftas seen in the drawing causes recess 29 to connect port 33 to port 34and recess 31 to connect port 36 to port 37. Movement of lever 25 in thereverse sense i.e. to the right as seen in the drawing will cause recess29 to connect port 33 to port 32 and recess 31 to connect port 37 toport 38. The port 33 is externally connected to steering control 39whilst port 37 is externally connected to steering control 41. Each ofthese steering controls comprises an adjustable leak valve whosestructure will be described more particularly with reference to FIGURE2.

The ports 32, 34, 36 and 38 are fed from an auxiliary pump 42 throughrespectively the restrictors 43, 44, 45 and 46. The ports 32 and 34 arealso connected through pipes 47 and 48 to the servo motor 17 foroverriding control thereof. Similarly the ports 36 and 38 are alsoconnected through pipes 49 and 51 to servo motor 16 for overridingcontrol thereof.

For operation of the control system as described in FIGURE 1 it will beseen that if forward speed of the tractor is selected by lever 25 bymovement to the left from a central position port 33 is connected toport 34 and port 36 is connected to port 37. This means that operationof the leak valve 39 permits flow of liquid from pump 42 throughrestrictor 44 and thus reduces pressure at pipe 48 relatively to thepipe 47. Similarly if valve 41 is operated flow of liquid takes placethrough restrictor 45 which will reduce pressure in pipe 49 relativelyto pipe 51. In this way the valve 39 can apply an overriding control toservo motor 17 in one particular direction only which is arranged to bereduction of the selected forward displacement of pump 16. Similarly ifvalve 41 is operated the pressure difference between pipes 49 and 51 issuch as to cause reduction in the selected forward displacement of pump5. When reverse speed of the tractor is selected by lever 25 to theright from the central position the valve plug 28 will connect ports 33and 32 together by the recess 29 and ports 37 and 38 together by therecess 31. Operation of leak valve 39 now causes liquid flow throughrestrictor 43 to reduce pressure in pipe 47 relatively to pipe 48,similarly operation of leak valve 41 will now cause reduction ofpressure in pipe 51 relatively to pipe 49. Thus it will be seen that thefunction of valve 26 is to reverse the operative action of the leakvalves 39 and 41 depending on whether forward or reverse speed isselected forward or reverse by lever 25 so that operation of either ofthese leak valves can only act to reduce the selected displacement givento either of the pumps and 6 by movement of the lever 25.

In control of the tractor incorporating the control arrangement ofFIGURE 1 the driver will select tractor speed by operation of the lever25. If he wishes to steer in one direction or the other he will operateeither the leak valves 39 or 41 and the vehicle will then move along acurved path determined by the actual reduction in selected displacementgiven to one or other of the pumps 5 or 6. This, of course, means thatone or the other tracks 11 or will move at a lower speed than the othertrack. The arrangement of the valves 39 and 41 on the vehicle is suchthat they are located on the side of the vehicle adjacent to the trackwhich they effectively control so that if the vehicle is to be turned tothe right the driver depresses the leak valve 41 on the right of thevehicle.

This will, of course, apply both for forward and reverse' movement ofthe vehicle.

Reference is now made to FIGURES 2 and 3 of the accompanynig drawingswhich illustrate the leak valves 39 and 41 in more detail. The valvesare enclosed in one body 52 having connectors 53 and 54 for connectionto the ports 33 and 37 of the valve 26. A return connection 55 isconnected to the hydraulic reservoir. From this valve body a pair oflevers 56 and 57 project for operation of the respective leak valves 39and 41. FIGURE 2 shows a cross section through one of these leak valvesas controlled by the lever 56. The lever 56 is pivoted at pivot pin 60and has a cam surface 58 for co-operation with a projecting plunger 59from the valve body 52. The plunger is slidably carried in a cylinder 61and at the outer end a seal 62 is provided to prevent escape of pressureliquid. The connection 54 has access to cylinder 61 at a pair of mainports 63 and at a pair of orifices 64 and 65. The orifices 64 and 65 arecontrolled by a land 66 on the plunger 59 for successive opening. Theseorifices when open permit flow of liquid through an axial passage 67 inthe plunger for escape into a chamber 68 in connection with thereservoir connection 55. The plunger 59 also includes a tapered portion69 which cooperates with the inner end 71 of the bore 61 so that withinward movement of the plunger 59 a leakage path in between port 63 andthe space 68 is opened up and increased. The end of the plunger 59within the chamber 68 acts on a compression spring 72 which opposesinward motion of the plunger 59 and normally acts to urge the plungeragainst the cam surface 58 of the lever 56 so that an abutment 73 of thelever rests against the body 52 of the valve. A further spring 74composed of Belleville washers co-operates with an abutment 75 withinthe chamber 68 so that at almost the complete movement of the plunger 59the Belleville washers engage the abutment 75 and further movement ispossible only by exerting a heavy force on the lever 56.

Reference is now made to the servo motor illustrated in FIGURE 4. Such aservo motor is provided for each of the pumps 5 and 6. This servo motoris disclosed in United States Patent 3,017,750 but a slight modificationhas been made which will be referred to further in this specification.This servo motor comprises a servo cylinder 76 within which a servopiston 77 is slidably mounted. A small diameter piston rod 78 extendsthrough one end of the cylinder 76 through a seal and is connected fordisplacement adjustment of the transmission pump with which itco-operates. In the position shown i.e. at midstroke, the transmissionpump is held at zero displacement, movement to the left in the drawinggiving forward displacement to the pump and movement to the right givingreverse displacement t0 the pump. Through the opposite end of thecylinder 76 a plunger 79 extends from piston 77, plunger 79 being ofconsiderably larger cross-section than piston rod 78. This permits ofthe left hand. working surface 81 of the piston 77 to be much larger ineffective area than the right hand working surface 82. A fluid pressureconnection 83 carries pressure liquid into the servo motor and this isconnected directly to the right hand end of cylinder 76 for operation onarea 82 of piston 77. The source of this servo liquid may convenientlybe pump 42 illustrated in FIGURE 1. Within the plunger 79 a controlvalve 84 is located which by longitudinal movement can operate toconnect pressure from the right hand end of cylinder 76 to the left handthereof through a passage 85 or alternatively it may connect the lefthand end of the cylinder 76 to reservoir pressure by connecting thepassage 85 to a central passage 86 within piston rod 78 which opens intothe casing of the associated transmission pump for return to reservoir.The valve 84 is moved for controlling piston 77 by means of a rod 87extending into a bore 88 within the right hand end of plunger 79. Themain control member 89 of the servo motor is slidably mounted within thebore 88 and projects from the right hand end thereof, a pin 91 beingprovided for connection either to the control rods 18 or 19 of FIG-URE 1. The portion 92 of the control member 89 which is slidably mountedwithin the bore 88 is capable of sliding a limited amount between theinner end 93 of bore 88 and an outer stop 94 on bore 88. The maindifference between the present construction and that disclosed in oursaid prior application concerns the amount of lost motion provided forthe control member. In the present construction this lost motion isconsiderably greater than in the said prior application. Within thecontrol member 89 a small diameter cylinder 95 is formed within which apiston 96 is slidably mounted. The rod 87 is integrally formed withpiston 96. A caged spring 97 is provided within a chamber 98 in controlmember 89 which is loaded between fixed stops 99 and 101 through themedium of loose stops 102 and 103 carried by the rod 87. The loose stopsare engaged between fixed stops 110 and 111 on the rod 87 by the actionof the spring 97. The function of the spring 97 is to ensure that apdedetermined pressure difference must exist on either side of piston 96before movement of the piston 96 can occur. A connector 104 extends fromthe right hand end of cylinder 95 whilst a connector 105 extends fromthe left hand. end of eylinder 95. For the transmission pump 6 theconnection 105 of the servo motor is connected to pipe 47 and connection104 is connected to pipe 48. For the transmission pump 5 the connector105 is connected to pipe 51 and the connection 104 is connected to pipe49.

Adjustment of a transmission pump displacement is effected through thecontrol member 89 and normally movement thereof is transmitted directlyto the rod 87 through the caged spring 97 if there is no pressuredifference between connections 104 and 105. Such movement will adjustvalve 84 to cause servo piston 77 to follow automatically and to adjustpump displacement correspondingly. In the event that a selecteddisplacement is to be reduced by operation of a leak valve 39 or 41 apressure difference will occur between the connections 104 and 105.Assume that forward displacement is selected and then that the leakvalve 39 is opened. The forward displacement selection will have movedthe control 89'and servo piston 77 to the left of the position in FIGURE4. Opening of the leak valve 39 will cause reduction in pressure at theport 34 and pipe 48 which reduces pressure at connection 104. This willcause piston 96 to move to the right when the loading of spring 97 isovercome. Such movement to the right will move valve 84 and cause servopiston 77 to move to reduce selected forward pump displacement. Suchmovement is, however, normally not transmitted to the control member 89because of the permitted lost motion of the sliding portion 92 in thecylinder 88. The amount of reduction of pressure at connection 104 willdetermine the amount of movement of piston 96 against the spring 97 andthus the amount of reduction of selected pump displacement. Referring tothe leak valve illustrated particularly in FIGURE 2 it will be seen thatinitial movement of the lever 56 will cause orifice 64 to be opened.This orifice is calibrated in conjunction with the restrictor 43 -or 44so that the drop in pressure obtained for small movement of the lever 56is sufficient to overcome the loading of spring 97 in the servo motor. Afurther movement of the lever 56 will cause slow escape of liquid to bepermitted by virtue of the increasing opening between the taper 69 andthe sharp edge 71 of bore 61. This will result in a further graduatedreduction in pressure with movement of lever 56 which will permitmovement of the piston 96 in conjunction with movement of lever '56.Thus the amount of depression of lever 56 will determine reduction ofrelated displacement of the associated transmission pump and thus thecurved path of movement of the tractor. If reverse displacement isselected by movement of lever 24 to the right from the FIGURE 1 positionand it is desired to turn to the same side of the vehicle the leak valve39 is operated by movement of the lever 56 and reduced pressure is thensupplied as a result to the connection 105 of the servo motor of pump 6.Selection of reverse movement will have caused displacement of servopiston 77 to the right from the FIGURE 4 position and reduction ofpressure at connection 105 will cause the auxiliary piston 96 to move tothe left to reduce the selected displacement. Similarly the other leakvalve 41 is operated by lever 57 in the event that it is desired to turntowards the side of the vehicle having track 11 whether forward orreverse movement is selected. For a considerable steering movement ofthe tractor during manoeuvering it may be necessary for one track to bemoved in the opposite direction to the other track so that in effect thetractor may move angularly on one spot without substantial forward orreverse movement. This effect is obtained by selecting a small forwardor reverse speed by lever 25 and then depressing the lever 56 or 57 aconsiderable amount to the extent that the Belleville Washers 74 contacttheir abutment 75 and the taper 69 will open a flow passage betweenconnection 54 and space 68. The resulting large reduction in pressure atconnection 104 now causes compression of spring 97 to the extent thatfollow up movement of piston 77 to reduce pump displacement causes meshoulder 93 which forms part of the plunger 79 to contact the slidingportion 92 of the control member 89. This will result in effectivelylocking together the control member 89 and the plunger 79 so thatmovement of the servo piston 77 cannot now cancel control movement givento the valve 84. The servo piston 77 will now tend to move toward theright hand limit of its movement in cylinder 76 as seen in FIGURE 4. Thedriver of the tractor would normally depress lever 56 to obtain suchmovement for a very short period in order to obtain a substantial speedreduction and even reversal of the track controlled by lever 56 or 57.Such full depression of lever 56 or 57 would not immediately result in alarge change of displacement of the associated pump because of the factthat the auxiliary pump 42 for supplying servo liquid to the servo motorconnector 83 is capable only of a limited supply of pressure liquid.

FIGURE 5 illustrates a modification of the invention disclosed inFIGURES 1 to 4. In FIGURE 5 a single steering control in the form of asteering wheel 106 is provided mounted on a rotary shaft 107. The shaftincludes a worm 108 meshing with a worm wheel sector 109. This sector ispivotally mounted in a casing 120 by means not shown and at a positionspaced from the gear teeth includes a cam shaped lobe 112. This lobeco-operates with the two leak valves 39 and 41 shown in FIGURE 1 whichare located at angularly spaced positions on either side of the lobe112. A lug 113 also carried by the gear segment 109 co-operates with twoabutments 114 and 115 which limit angular movement of the sector 109.The valves 39 and 41 are angularly spaced about the axis of the sector109 by an amount equal to the angular extent of the lobe 112. As shownin FIGURE 5 the sector 109 is so set that neither leak valve 39 or 41 isoperated to ensure that the tractor will travel along a straight path.Movement of the steering wheel 106 in either direction will causeoperation of one or other of the valves 39 or 41 to reduce the speed ofone or other of the tracks and so cause the tractor to travel along acurved path. The arrangement as shown in FIGURE 5 has the particularadvantage that it prevents simultaneous operation of both valves 39 and41.

I claim as my invention:

1. In combination, a vehicle having two ground-engaging elements spacedtransversely thereof, a power source for driving the vehicle, a pair ofinfinitely variable speed ratio hydraulic power transmissionsinterconnecting the ground-engaging elements with the power source, apair of movable secondary speed controls connected to the transmissionsto vary the speed ratios thereof, a primary speed control connected tothe secondary speed controls to select a common speed ratio for thetransmissions, and a pair of steering controls connected to thesecondary speed controls to effect overriding adjustments in the speedratios of the transmissions, there being overrid-er means in theconnections between the secondary speed controls and the primary speedcontrol permitting the secondary speed controls to move individually inrelationship to the primary speed control, said primary speed controlhaving movable intermediate controls connected therewith, and saidsecondary speed controls including pairs of movable servo and followercontrols, the former of which are connected with the intermediatecontrols by the overrider means and individually responsive to theoperation of the steering controls to move in relation to theintermediate controls, and the latter of which are connected with thetransmissions and individually responsive to the operation of the servocontrols to follow the movements thereof, there being connectionsbetween the intermediate controls and the follower controls limiting themovements of the follower controls in relation to the intermediatecontrols to less than the movements permitted the servo controls inrelation to such intermediate controls by the overrider means, so thatthe follower controls interlock with the intermediate controls aftersmall overriding adjustments in the speed ratios of the transmissions,and additional overrider means in the connections between theintermediate controls and the primary speed control permitting theintermediate controls to move individually in relation to the primaryspeed control, so that the follower controls and the intermediatecontrols can move together for larger overriding adjustments in thespeed ratios of the transmissions.

2. The combination according to claim 1 wherein the transmissionsinclude a pair of hydraulic pumps which have infinitely variabledeliveries that determine the speed ratios of the transmissions, andwherein the follower controls are connected with the pumps to vary thedeliveries thereof.

3. The combination according to claim 1 wherein the follower controlsare hydraulically operated and the servo controls include a pair ofcontrol valves in the hydraulic systems of the follower controls.

4. The combination according to claim 1 wherein the servo controls arehydraulically operated and the steering controls include a pair of leakvalves in the hydraulic systems of the servo controls.

5. The combination according to claim 4 further comprising a directionvalve which is conjointly operable with the primary speed control anddisposed in the hydraulic systems of the servo controls, intermediatethe leak valves and the servo controls, to interconnect the leak valveswith their corresponding servo controls such that the direction of speedratio adjustment effected by the steering controls is opposed to thateffected by the primary speed control.

References Cited by the Examiner UNITED STATES PATENTS 2,941,609 6/1960Bowers et al. ISO-6.48 3,024,858 3/1962 Davis et al. ISO-6.48 3,025,6733/1962 Brown et al. 1806.48 X

BENJAMIN HERSH, Primary Examiner.

J. A. PEKAR, Assistant Examiner.

1. IN COMBINATION, A VEHICLE HAVING TWO GROUND-ENGAGING ELEMENTS SPACEDTRANSVERSELY THEREOF, A POWER SOURCE FOR DRIVING THE VEHICLE, A PAIR OFINFINITELY VARIABLE SPEED RATIO HYDRAULIC POWER TRANSMISSIONSINTERCONNECTING THE GROUND-ENGAGING ELEMENTS WITH THE POWER SOURCE, APAIR OF MOVABLE SECONDARY SPEED CONTROLS CONNECTED TO THE TRANSMISSIONSTO VARY THE SPEED RATIOS THEREOF, A PRIMARY SPEED CONTROL CONNECTED TOTHE SECONDARY SPEED CONTROLS TO SELECT A COMMON SPEED RATIO FOR THETRANSMISSIONS, AND A PAIR OF STEERING CONTROLS CONNECTED TO THESECONDARY SPEED CONTROLS TO EFFECT OVERRIDING ADJUSTMENTS IN THE SPEEDRATIOS OF THE TRANSMISSIONS, THERE BEING OVERRIDER MEANS IN THECONNECTIONS BETWEEN THE SECONDARY SPEED CONTROLS AND THE PRIMARY SPEEDCONTROL PERMITTING THE SECONDARY SPEED CONTROLS TO MOVE INDIVIDUALLY INRELATIONSHIP TO THE PRIMARY SPEED CONTROL, SAID PRIMARY SPEED CONTROLHAVING MOVABLE INTERMEDIATE CONTROLS CONNECTED THEREWITH, AND SAIDSECONDARY SPEED CONTROLS INCLUDING PAIRS OF MOVABLE SERVO AND FOLLOWERCONTROLS, THE FORMER OF WHICH ARE CONNECTED WITH THE INTERMEDIATECONTROLS BY THE OVERRIDER MEANS AND INDIVIDUALLY RESPONSIVE TO THEOPERATION OF THE STEERING CONTROLS TO MOVE IN RELATION TO THEINTERMEDIATE CONTROLS, AND THE LATTER OF WHICH ARE CONNECTED WITH THETRANSMISSIONS AND INDIVIDUALLY RESPONSIVE TO THE OPERATION OF THE SERVOCONTROLS TO FOLLOW THE MOVEMENTS